1. Field of the Invention
The invention relates to the providing of packet data access services in a communication system. Particularly, the invention relates to a method for the routing and control of packet data traffic in a communication system.
2. Description of the Related Art
The amount of packet data traffic continues to increase with the introduction of new multimedia services. It becomes important for packet data access networks to be able to transmit packet data in an efficient and a scalable way that avoids introducing bottlenecks to the architecture of the network. However, simultaneously it must be possible to control the packet data traffic and to apply a variety of policies for the packet data traffic. It must be possible to control the attaching of users to different sub-networks, for instance, in the form of deciding on the providing of addresses from a given access point only to authorized users. The routing and policy control must be efficient irrespective of the type of an access network.
A problem associated with prior art networks is that the burden of the routing of packet data traffic and the interfacing of external networks for the packet data traffic has been centralized to network elements in the same position in the network topological without taking into consideration the type of packet data traffic or the type of access network used.
Reference is now made to FIG. 1, which illustrates a Universal Mobile Telecommunications System (UMTS) and an IP multimedia Subsystem (IMS) in prior art. The IP multimedia architecture for UMTS and GPRS mobile communication networks is referred to as an IP Multimedia Subsystem (IMS). The IMS is defined in the 3G Partnership Project (3GPP) specification 23.228 version 6.14.0, June 2006. The GPRS is defined in the 3GPP specification 23.060, version 6.13.0, June 2006. In FIG. 1 there is shown a mobile station 100, which communicates with a Radio Network Controller (RNC) 114 within a Radio Access Network 110. The communication occurs via a Base Transceiver Station (BTS) 112. The radio access network 110 is, for example, a 2G GSM/EDGE radio access network or a 3G UMTS radio access network. An IP Connectivity Access Network (IP-CAN) functionality connected to access network 110 comprises at least a Serving GPRS Support Node (SGSN) 122 and a Gateway GPRS Support Node (GGSN) 124. An IP connectivity access network can also been seen as to comprise both a packet switched core network functionality 120 and an access network 110. The main issue is that an IP-CAN provides IP connectivity to user terminals towards an IP network such as the Internet or an Intranet. SGSN 122 performs all mobility management related tasks and communicates with a Home Subscriber Server (HSS) 160 in order to obtain subscriber information. GGSN 124 provides GPRS access points. There is an access point, for example, to a Media Gateway (MGW) 126, to a first router 142 attached to an IP network 140, and to a Proxy Call State Control Function (P-CSCF) 152. The access point to IP network is used to relay packets to/from an IP network node (IP-N) such as 147. The packets may be related to, for example, Internet browsing or File Transfer Protocol (FTP) file transfer. The access point for P-CSCF 152 is used to convey signaling traffic pertaining to IP multimedia. GGSN 124 establishes Packet Data Protocol (PDP) contexts, which are control records associated with a mobile subscriber such as mobile station 100. A PDP context provides an IP address for packets received from or sent to mobile station 100. A PDP context has also associated with it a UMTS bearer providing a certain QoS for mobile station 100. In GGSN 124 there is a primary PDP context for the signaling packets associated mobile station 100. For the user plane data packets carrying at least one IP flow there is established at least one secondary PDP context. The at least one IP flow is established between a calling terminal and a called terminal in association with an IP multimedia session. An IP flow carries a multimedia component, in other words a media stream, such as a voice or a video stream in one direction. For voice calls at least two IP flows are required, one for the direction from the calling terminal to the called terminal and one for the reverse direction. In this case an IP flow is defined as a quintuple consisting of a source port, a source address, a destination address, a destination port and a protocol identifier.
The communication system illustrated in FIG. 1 comprises also the IP Multimedia Subsystem (IMS) functionality. The IMS is used to set-up multimedia sessions over IP-CAN. The network elements supporting IMS comprise at least one Proxy Call State Control Function (P-CSCF), at least one Inquiring Call State Control Function (I-CSCF), at least one Serving Call State Control Function S-CSCF, at least one Brakeout Gateway Control Function (BGCF) and at least one Media Gateway Control Function (MGCF). As part of the IMS there is also at least one Home Subscriber Server (HSS). Optionally, there is also at least one Application Server, which provides a variety of value-added services for mobile subscribers served by the IP multimedia subsystem (IMS).
P-CSCF 152 receives signaling plane packets from GGSN 124. Session Initiation Protocol (SIP) signaling messages are carried in the signaling plane packets. The signaling message is processed by P-CSCF 152, which determines the correct serving network for the mobile station 100 that sent the signaling packet. The determination of the correct serving network is based on a home domain name provided from mobile station 100. Based on the home domain name is determined the correct I-CSCF, which in FIG. 1 is I-CSCF 154. I-CSCF 154 hides the topology of the serving network from the networks, in which mobile station 100 happens to be roaming. I-CSCF 154 takes contact to home subscriber server 160, which returns the name of the S-CSCF, which is used to determine the address of S-CSCF 156 to which the mobile station 100 is to be registered. If I-CSCF 156 must select a new S-CSCF for mobile station 100, home subscriber server 160 returns required S-CSCF capabilities for S-CSCF selection.
Upon receiving a registration, S-CSCF 156 obtains information pertaining to the profile of the mobile station 100 from HSS 160. The information returned from HSS 160 may be used to determine the required trigger information that is used as criterion for notifying an application server 162. The trigger criteria are also referred to as filtering criteria. Application server 162 may be notified on events relating to incoming registrations or incoming session initiations. Application server 162 communicates with S-CSCF 156 using the ISC-interface. The acronym ISC stands for IP multimedia subsystem Service Control interface. The protocol used on ISC interface is SIP. AS 162 may alter SIP INVITE message contents that it receives from S-CSCF 156. The modified SIP INVITE message is returned back to S-CSCF 156.
If the session to be initiated is targeted to a PSTN subscriber or a circuit switched network subscriber, the SIP INVITE message is forwarded to a BGCF 158. BGCF 158 determines the network in which interworking to PSTN or the circuit switched network should be performed. In case PSTN interworking is to be performed in the current network, the SIP INVITE message is forwarded to MGCF 159 from BGCF 158. In case PSTN interworking is to be performed in another network, the SIP INVITE message is forwarded from BGCF 158 to a BGCF in that network (not shown). MGCF 159 communicates with MGW 126. The user plane packets carrying a media bearer or a number of interrelated media bearers for the session are routed from GGSN 124 to MGW 126 as illustrated in FIG. 1.
If the session to be initiated is targeted to a terminal 146, which is a pure IP terminal, S-CSCF 156 forwards the SIP INVITE message to terminal 146. Terminal 146 communicates with a second router 144, which interfaces IP network 140. IP network 140 is used to carry the user plane IP flows associated with the session established between mobile station 100 and terminal 146. The user plane IP flows between first router 142 and GGSN 124 are illustrated with line 128. The user plane IP flows between second router 144 and terminal 146 are illustrated with line 148.
Generally, in FIG. 1 user plane is illustrated with a thick line and control plane with thinner line.
One problem in the architecture illustrated in FIG. 1 is, for example, that if there are other types of IP-CANs (not shown) that are used to access IMS 150 or the amount of user plane traffic grows by way of a myriad of IP multimedia sessions specifically GGSN 124 may be required to process significant packet data traffic. Therefore, it would be beneficial to have an architecture, which may provide for access point gateway functionality at different points in the network topology and avoids the buildup of network bottlenecks.